Method of increasing mass transfer rate of acid gas scrubbing solvents

ABSTRACT

A method of increasing the overall mass transfer rate of acid gas scrubbing solids is disclosed. Various catalyst compounds for that purpose are also disclosed.

This application is a division of U.S. patent application Ser. No.13/853,292 filed 29 Mar. 2013, now U.S. Pat. No. 9,409,125.

TECHNICAL FIELD

The present invention relates generally to various methods of increasingthe overall mass transfer rate of acid gas scrubbing solvents utilizingvarious catalysts compounds.

BACKGROUND

The cleanup of acid gasses or sour gas, such as CO₂ in particular, fromnatural gas and in oil refining has been an extensively practicedtechnology. The industrial removal of CO₂ from natural gas dates back tothe 1930's. In the 21^(st) century, due to the potential impact ofanthropogenic CO₂ emissions on the climate, post-combustion CO₂ capturehas gained tremendous attention. While several technologies exist forthe removal of acid gasses one of the most commonly employed practicesis the use of aqueous amines. Of these amines, tertiary amines are oftenused for natural gas applications due to their low energy ofregeneration. For post-combustion CO₂ capture applications primary andsecondary amines tend to be in part favored by their faster rate at thelow CO₂ driving force condition. Regardless of the application, the masstransfer rate in the absorber column dictates the size of the column(capital cost) used and, consequently, has a substantial impact on theoverall process cost. An overall process depicting a thermal swingprocess is presented in FIG. 1. An aqueous amine solution is circulatedbetween the absorber 10 and stripper 12. The gas, containing CO₂, entersthe bottom of the absorber where it contacts the aqueous amine absorbentremoving it from the gas stream. The liquid solution, CO₂ rich aminesolution, is then passed through a heat exchanger 14 to improveefficiency before being heated to a higher temperature in the stripper12. The stripper 12 removes the CO₂ as a gas from the amine solution toproduce a lean, or CO₂ deficient solution. The lean solution is returnedto the absorber 10 by way of the heat exchanger 14 to repeat theprocess.

In order to minimize system capital (absorber cost) it is important tomaximize the overall mass transfer rate for the scrubber system as thereis a direct correlation between the two. This invention relates tomethods for this purpose as well as to catalyst compounds useful inthose methods.

SUMMARY

A method is provided for increasing the overall mass transfer rate ofacid gas scrubbing solvents. The method comprises adding a catalystcompound to a fluid stream including an acid gas and an acid gasscrubbing solvent wherein that catalyst compound has a chemical formula:

where:

(a) M is any group VII B through XII B element;

(b) E is any combination of N, O, S having a net 2⁻ charge perindividual ligand;

(c) R_(1, 2, 4)═—H, —COOH, —[OCH₂CH₂]_(n)—OR₉, CH₃, amine, amide,phosphate, —OH, —R₅OH, —[SO₃]⁻;

(d) R₃═—H, —COOH, —[OCH₂CH₂]_(n)—OR₉, amine, amide, phosphate, —OH,—R₅OH, —[SO₃]⁻, —[(CH₂)_(n)Q]⁺[A]⁻;

(e) R₅═C₁-C₅ alkyl; (f) A=monovalent anion: Cl, Br, I, F, PF₆, BF₄,acetate, trifluoroacetate, ClO₄, NO₃;

(g) Q=monovalent cation: PX₃ where X=alkyl, cyclic alkyl, aryl, O-alkyl,O-aryl, N(R₆)₃ where R₆=alkyl, cyclic alkyl, N-heterocyclic ring,imidazole;

(h)

where Y═—H, —COOH, —R₇OOH (R₇=alkyl ranging from 2-10 carbons);

—[OCH₂CH₂CH₂]_(n)—OR₉; —OH; —SO₃; —NO₂; amine, amide; or

where Z₁₋₆═—H, any alkyl, —COOH, —R₈OOH (R₈=alkyl ranging from 2-10carbons), —[OCH₂CH₂]_(n)—OR₉; OH; SO₃; NO₂; amine, amide; and

(i) where n=1 to 10; and

(j) R₉═H or alkyl.

In one possible embodiment the catalyst compound has a chemical formula:

where R=any alkyl

M=Co, Zn.

In another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn

R=any alkyl.

In still another possible embodiment the catalyst compound has achemical formula:

where M=Co, Zn.

In yet another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In yet another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In still another possible embodiment the catalyst compound has achemical formula:

where M=Co, Zn.

In any of the embodiments the acid gas scrubbing solvent includes anamine or a mixture of amines. In one possible embodiment the acid gasscrubbing solvent includes a mixture of (a) a promoter amine and (b) atertiary amine.

In one possible embodiment the acid gas scrubbing solvent includeschemical compounds selected from a group including but not limited to,monoethanolamine (MEA), 1-amino-2-propanol (1A2P), 3-amino-1-propanol,2-amino-1-propanol, 2-amino-1-butanol, 1-amino-2-butanol,3-amino-2-butanol, 2-(methylamino)ethanonol (MAE),2-(ethylamino)ethanol, morpholine, piperazine (PZ), 1-methylpiperazine(NMP), 2-methylpiperazine, hydroxypiperadine, 2-piperidineethanol,N-aminoethylpierazine (AEP), aminopropylmorpholine, 4-aminopiperidine,2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA),diisopropanolamine (DIPA), glycine, alanine, β-alannine, sarcosine,ethylene diamine (EDA), 1,3-propanediamine, 1,4-butanediamine,1,5-pentanediamine, 1,6-hexanediamine, methyldiethanolamine (MDEA),triethanolamine (TEA), dimethylethanolamine (DMEA),N,N,N′,N′-tetramethyl-1,8-naphthalenediamine, diethylmonoethanolamine,dipropylmonoethanolamine, 1,4-dimethylpiperazine, NN,N′,N′-tetramethyl-1,6-hexanediamine,N,N,N′N′-tetrakis(2-hydroxyethyl)ethylenediamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethylpropane-1,3-diamine,N,N,N′,N′-tetramethylbutane-1,4-diamine,N,N,N′,N′-tetramethyl-1,5-pentanediamine, alkali carbonate, and mixturesthereof.

Further the catalyst compound is provided at a concentration of betweenabout 0.05 mM and about 100 mM.

Various catalyst compounds are also claimed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawings incorporated herein and forming a part of thespecification, illustrate several aspects of the present method andtogether with the description serve to explain certain principlesthereof. In the drawings:

FIG. 1 is a schematical illustration of a process for removing acid gasfrom a fluid stream utilizing solvent and thermal swing regeneration.

FIG. 2 is a schematical illustration of a simple CO₂ bubbling apparatusused for catalyst testing.

FIG. 3 is a graphical illustration of removal rate versus carbon loadingfor various catalysts used with 30 wt % MEA at 40° C.

FIG. 4 is a graphical illustration of removal rate versus carbon loadingfor various catalysts in 20% 1-amino-2-propanol solvent with 13% CO₂ at40° C.

FIG. 5 is a schematical illustration of a wetted wall column (WWC)apparatus used in testing the catalysts.

FIG. 6 is a graphical comparison of CO₂ overall mass transfer asmeasured on a wetted wall column for 30 wt % MEA at 40° C. with catalystCAER—CIP and CAER—C3I.

DETAILED DESCRIPTION

This document relates generally to methods of increasing overall masstransfer rate of acid gas scrubbing solvents as well as to noveltransition metal monomer complexes incorporating a single transitionmetal atom.

The method may be broadly described as comprising adding a catalystcompound to a fluid stream including an acid gas and an acid gasscrubbing solvent. The catalyst compound has a chemical formula:

where:

(a) M is any group VII B through XII B element;

(b) E is any combination of N, O, S having a net 2⁻ charge perindividual ligand;

(c) R_(1, 2, 4)═—H, —COOH, —[OCH₂CH₂]_(n)—OR₉, amine, amide, phosphate,—OH, —R₅OH, —[SO₃]⁻;

(d) R₃═—H, —COOH, —[OCH₂CH₂]_(n)—OR₉, amine, amide, phosphate, —OH,—R₅OH, R₅OH, —[SO₃]⁻, —[(CH₂)_(n) Q]⁺[A]⁻;

(e) R₅═C₁-C₅ alkyl;

(f) A=monovalent anion: Cl, Br, I, F, PF₆, BF₄, acetate,trifluoroacetate, ClO₄, NO₃;

(g) Q=monovalent cation: PX₃ where X=alkyl, cyclic alkyl, aryl, O-alkyl,O-aryl, N(R₆)₃ where R₆=alkyl, cyclic alkyl, N-heterocyclic ring,imidazole;

(h)

where Y═—H, —COOH, —R₇OOH (R₇=alkyl ranging from 2-10 carbons);

—[OCH₂CH₂]_(n)—OR₉; —OH; —SO₃; —NO₂; amine, amide; or

where Z₁₋₆═—H, any alkyl, —COOH,—R₈OOH (R₈=alkyl ranging from 2-10carbons), —[OCH₂CH₂]_(n)—OR₉; OH; SO₃; NO_(2;) amine, amide;

(i) where n=1 to 10; and

(j) R₉═H or alkyl.

In one particular embodiment the catalyst compound has a chemicalformula:

where R=any alkyl

M=Co, Zn.

In another particular embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn

R=any alkyl.

In another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In yet another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In yet another possible embodiment the catalyst compound has a chemicalformula:

where M=Co, Zn.

In still another possible embodiment the catalyst compound has achemical formula:

where M=Co, Zn.

For any embodiment of catalyst compound, the terms “alkyl” or “anyalkyl”, when not otherwise stipulated, include at least C₂-C₁₀ alkylcompounds.

For any of the method embodiments the acid gas scrubbing solvent mayinclude an amine. In one possible embodiment the acid gas scrubbingsolvent includes a mixture of (a) a promoter amine, selected from agroup of primary and secondary amines and (b) a tertiary amine.

Such a mixture is described in detail in copending U.S. patentapplication Ser. No. 13/853,186, filed on Mar. 29, 2013 and entitled“Solvent and Method for Removal of an Acid Gas from a Fluid Stream”, thefull disclosure of which is incorporated herein by reference. Promoteramines useful in the present method include, but are not limited to, theprimary and secondary amines such as 3-N-sulfonylamine (SA),3-aminopropionitrile (APN), diethyl 2-aminoethanephosphonate (EtP2),N-methyltetrahydrothiophen-3-amine 1,1-dioxide,2,2′-sulfonyldiethanamine, 3,3′-sulfonyldipropaneamine,4,4′-sulfonyldibutanenamine, 2-aminoethyl methyl sulfone,4-aminobutanenitrile, 6-aminohexanenitrile,3-(methylamino)propanenitrile, diethyl[2-(methylamino)ethyl]phosphonate, diethyl (3-aminopropyl)phosphonate,diethyl (4-aminobutyl)phosphonate, diethyl (5-aminopentyl)phosphonate,diethyl (6-aminohexyl)phosphonate, 2-(tert-butoxy)ethan-1-amine,N-methyl-2-[(2-methyl-2-propanyl)oxy]ethanamine and mixtures thereof.

Tertiary amines and carbonate based salts useful in the present methodinclude but are not limited to methyldiethanolamine (MDEA),triethanolamine (TEA), N,N,-dialkylethanolamine,N,N,N′N′-tetraalky-1,8-naphthalenediamine, N,N, -dialkylbenzylamine,1,4-dialkylpiperazine, N,N,N′,N′-tetraalkyl-1,6-hexanediamine,N,N,N′N′-tetraalkyl-1,5-pentanediamine,N,N,N′N′-tetraalkyl-1,4-butanediamine,N,N,N′N′-tetraalkyl-1,3-propanediamine,N,N,N′,N′-tetraalkyl-1,2-ethanediamine, N,N,N′N′-tetrakis(2-hydroxyethyl)ethylenediamine,N,N,N;N;N″-pentaalkyldiethylenetriamine,N,N,N′,N′,N″-pentaalkyldipropylaminetriamine, N,N,-dialkylcyclohexylamine, N,N,N′,N′-tetraalkylbis(aminoethyl)ether,N,N,-dimethyl-2(2-aminoethoxy)ethanol, alkali carbonates where alkylrepresents any methyl, ethyl, propyl, butyl isomer, and mixturesthereof. In one possible embodiment, the catalyst compound is providedin the fluid stream with a concentration of between about 0.05 mM andabout 50 mM. In another possible embodiment the catalyst compound isprovided in the fluid stream with a concentration of between 50.1 mM and75 mM. In yet another possible embodiment the catalyst compound isprovided in the fluid stream with a concentration of between about 75.1mM and 100 mM.

Primary and secondary amines useful in the present method include butare not limited to monoethanolamine (MEA), 1-amino-2-propanol (1A2P),3-amino-1-propanol, 2-amino-1-propanol, 2-amino-1-butanol,3-amino-2-butanol, 1-amino-2-butanol, 2-(alkylamino)ethanonol (MAE),diglycolamine, morpholine, piperazine (PZ), 1-methylpiperazine (NMP),2-methylpiperazine, hydroxypiperadine, hydroxymethylpiperazine,2-piperidineethanol, N-aminoethylpierazine (AEP), aminopropylmorpholine,4-aminopiperidine, 3-aminopiperidine, 2-amino-piperidine,diethanolamine, 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA),diisopropanolamine (DIPA), glycine, alanine, 13-alannine, sarcosine,isopropanolamine, benzylamine, ethylene diamine (EDA),1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine,1,6-hexanediamine.

In any of the embodiments, the catalyst compound must be stable underthe relatively high temperature conditions (e.g. between perhaps 70 and170° C.) found within the stripper 12. The present catalyst compoundsmeet this requirement.

The following examples further illustrate how to synthesize ormanufacture certain representative catalysts used in the method ofincreasing the overall mass transfer rate of acid gas scrubbingsolvents.

EXAMPLE 1

Preparation of H₂LP: To a solution of1-(3-formyl-4-hydroxybenzyl)triphenylphosphoniumchloride (5.00 g, 11.55mmol) in dry ethanol (40 mL) was added ethylenediamine (0.40 mL, 6 mmol)slowly at room temperature. The resulting solution was stirred at refluxtemperature for 3 h. The solution was allowed to cool to roomtemperature and the solvent was removed under reduced pressure. Theyellow residue was dissolved in dichloromethane (50 mL) and slowly addeddropwise to 150 mL of stirring ethyl acetate to give a bright yellowpowder which was collected via filtration (4.9958 g, 97%) in >95% puritybased on ¹H NMR spectroscopy.

Preparation of CAER-ClP: A 100-mL round-bottom flask was charged withH₂LP (4.594 g, 5.17 mmol) and CoCl₂.(H₂O)₆ (1.3541 g, 5.7 mmol), andEtOH (40 mL) was added to make a slurry. 2 equiv. of Et₃N (1.5 mL, 11mmol) was added and the mixture was heated at reflux for 3 hours. Themixture was cooled to room temperature and the solvent was removed underreduced pressure to give a brown powder. The brown powder was washedwith ice cold water to remove ammonium salts and then triturated withether to give the desired product as a brown solid (3.2295 g, 63%)

EXAMPLE 2

Preparation of H₂LI: To a solution of1-(3-formyl-4-hydroxybenzyl)-3-methylimidazolium hexafluorophosphate(5.00 g, 13.80 mmol) in dry ethanol (40 mL) was added ethylenediamine(0.50 mL, 7.5 mmol) slowly at room temperature. The resulting solutionwas stirred at reflux temperature for 6 h. The solution was allowed tocool to room temperature after which a solid separated out. The solidwas washed with ethanol (3×5 mL) then ether (3×10 mL) and dried in vacuoto give a yellow solid (5.4375 g, 97%) in >95% purity based on ¹H NMRspectroscopy.

Preparation of CAER-C3I: A 100-mL round-bottom flask was charged withH₂LI (5.011 g, 6.68 mmol) and ZnCl₂ (1.3630 g, 10 mmol), and EtOH (40mL) was added to make a slurry. 2 equiv. of Et₃N (2.0 mL, 14 mmol) wasadded and the mixture was heated at reflux for 3 hours. The mixture wascooled to room temperature and a pale yellow solid was collected viafiltration (4.6390 g, 85%) in >95% purity based on ¹H NMR spectroscopy.

EXAMPLE 3

Preparation of H₂LP*: A 100-mL round-bottom flask was charged with5-chloromethyl-2-hydroxybenzaldehyde (10.3327 g, 60.4 mmol) anddissolved in ethyl acetate (40 mL) and triethylphosphite (11.5 mL, 67mmol) was added. The mixture was heated at reflux (80° C.) for 3 hours.The mixture was cooled to room temperature and the solvent removed underreduced pressure to give triethoxy(3-formyl-4-hydroxybenzyl)phosphoniumchloride as a viscous oil which was used without further purification.The viscous oil (10.003 g, 30 mmol) was dissolved in ethanol (40 mL) andethylenediamine (1.2 mL, 18 mmol) was added slowly. The mixture washeated at reflux (80° C.) for 3 hours. The mixture was cooled to roomtemperature and the solvent was removed under reduced pressure to give athick, yellow, oily substance. The oil was washed with ether (3×10 mL).The ether was evaporated slowly over 24 hours to produce a thick,yellow, viscous oil (10.2215 g, 98%) in ˜85% purity based on ¹H NMRspectroscopy.

Preparation of CAER-C3P*: A 100-mL round-bottom flask was charged withH₂LP* (5.028 g, 7.2 mmol) and ZnCl₂ (1.4652 g, 10.8 mmol), and dissolvedin EtOH (40 mL). 2 equiv. of Et₃N (2.1 mL, 15 mmol) was added and themixture was heated at reflux for 3 hours. The mixture was cooled to roomtemperature and the solvent was removed under reduced pressure to give athick, oily substance. The oil was washed with ether (3×10 mL) toproduce a white solid which was removed via filtration. The ether wasevaporated slowly over 24 hours to produce a thick, colorless, viscousoil (4.8832 g, 89%) in >90% purity based on ¹H NMR spectroscopy.

EXAMPLE 4

Preparation of H₂L4: A 50 mL round bottom flask was charged with 2equiv. 4-formyl-3-hydroxybenzoic acid (0.2471 g, 1.49 mmol) anddissolved in EtOH followed by addition of 1 equiv. ethylenediamine (50μL, 0.75 mmol). The mixture was heated at reflux for 2 hr. The reactionmixture was cooled to room temp. and a yellow powder was collected viafiltration (247.3 mg, 93%) >95% purity based on ¹H NMR spectroscopy.

Preparation of CAER-C4: A 100-mL round-bottom flask was charged withH₂L4 (0.06980 g, 0.196 mmol) and ZnCl₂ (0.0433 g, 0.318 mmol), and EtOHwas added to make a slurry. 2 equiv. of Et₃N (58 μL, 0.417 mmol) wasadded and the mixture was heated at reflux for 3 hours. The mixture wascooled to room temperature and a pale yellow solid was collected viafiltration (66.7, 81%) in >95% purity based on ¹H NMR spectroscopy.

EXAMPLE 5

Preparation of H₂L5: A 100-mL round bottom flask was charged with3,4-diaminobenzoic acid (2.0067 g, 13.2 mmol) and dissolved in EtOH. 2equiv. salicylaldehyde (2.8 mL, 26.3 mmol) was added and the reactionmixture was heated at reflux for 2 hr, at which point an orange solidhad formed. The mixture was cooled to room temp. and the orange solidwas collected via filtration (1.8274, 38%). The orange filtrate wasstored at 8° C. for 15 hours and a second crop of orange solids wascollected via filtration (2.3211 g, 48%), for a combined 86% yieldin >95% purity based on ¹H NMR spectroscopy.

Preparation of CAER-05_(z): A 100-mL round-bottom flask was charged withH₂L5 (0.4921 g, 1.37 mmol) and ZnCl₂ (0.3224 g, 2.37 mmol), and EtOH wasadded to make a slurry. 2 equiv. of Et₃N (390 μL, 2.8 mmol) was addedand the mixture was heated at reflux for 3 hours. The mixture was cooledto room temperature and a pale yellow/orange solid was collected viafiltration (0.5613, 97%) in >95% purity based on ¹H NMR spectroscopy.

EXAMPLE 6

Preparation of CAER-C1: A 100-mL round-bottom flask was charged withH₂LI (3.023 g, 4.04 mmol) and CoCl₂.(H₂O)₆ (1.0641 g, 4.44 mmol), andEtOH (40 mL) was added to make a slurry. 2 equiv. of Et₃N (1.2 mL, 8.63mmol) was added and the mixture was heated at reflux for 3 hours. Themixture was cooled to room temperature and a dark brown solid wascollected via filtration (3.592 g, 93%).

EXAMPLE 7

Preparation of CAER-C3P: A 100-mL round-bottom flask was charged withH₂LP (5.002 g, 5.63 mmol) and ZnCl₂ (1.3630 g, 10 mmol), and EtOH (40mL) was added to make a slurry. 2 equiv. of Et₃N (1.75 mL, 12 mmol) wasadded and the mixture was heated at reflux for 3 hours. The mixture wascooled to room temperature and a pale yellow solid was collected viafiltration (4.9790 g, 93%) in >95% purity based on ¹H NMR spectroscopy.

Catalyst Testing in Concentrated Primary Amines: Breakthrough Method

A schematic of the apparatus used is shown in FIG. 2. Briefly, 0.85L/min feed gas containing ˜13% CO₂ mixed with N₂ is firstly saturatedwith water in the first impinger and then bubbled through 15 ml oftesting solvent in the second impinger. Both the saturator and bubblerare immersed in a water bath at 40° C. The gas effluent is dried throughan ice condenser and a Drierite tube before it is analyzed for CO₂concentration using a dual-beam NDIR online CO₂ analyzer (Model 510,HORIBA, Ltd). Data of CO₂ outlet concentration with respect to time iscontinuously recorded through a LABVIEW® package with 1 second interval.A line that bypasses the saturator and the bubbler is set up for inletCO₂ concentration determination. Before each experiment, the alkalinityof the testing solvent is precisely determined through acid-basetitration.

The difference of inlet and outlet CO₂ concentration represents theabsorbed amount of CO₂ at a particular time. The integration of theconcentration difference represents the CO₂ loading as expressed

$\begin{matrix}{{{CO}_{2}\mspace{14mu}{{Loading}(t)}\left( {{mol}\mspace{14mu}{CO}_{2}\text{/}{kg}\mspace{14mu}{solution}} \right)} = \frac{\int_{0}^{t}{\left( {C_{in} - {C_{out}(t)}} \right)d\; t}}{m_{sol}}} & {{Eq}\mspace{14mu} 1}\end{matrix}$in which G_(in) is the CO₂ feed gas rate in mol/s, C_(out) is the CO₂effluent rate in mol/s, t is the time in second, and mol is the mass ofsolution in kg. The CO₂ loading at G_(out)=G_(in) is the equilibrium CO₂capacity at 13% CO₂ and 40° C. With the alkalinity (mol N/kg ofsolution) of the solution known, the CO₂ loading can also be written as

$\begin{matrix}{\alpha = {\frac{{{CO}2}\mspace{14mu}{{Loading}\left( {{mol}\mspace{14mu}{CO}_{2}\text{/}{kg}\mspace{14mu}{solution}} \right)}}{{Alkalinity}\left( {{mol}\mspace{14mu} N\text{/}{kg}\mspace{14mu}{solution}} \right)} = \frac{{mole}\mspace{14mu}{of}\mspace{14mu}{CO}_{2}}{{mole}\mspace{14mu}{of}\mspace{14mu} N}}} & {{Eq}\mspace{14mu} 2}\end{matrix}$

In addition, the absorption rate can be described by the derivate of CO₂loading with respect to time:

$\begin{matrix}{{{Absorption}\mspace{14mu}{{rate}\left( {{mol}\mspace{14mu}{CO}_{2}\text{/}{kg}\mspace{14mu}{solution}\text{/}s} \right)}} = \frac{d\;{CO}_{2}\mspace{14mu}{Loading}}{d\; t}} & {{Eq}\mspace{14mu} 3}\end{matrix}$

As illustrated in FIGS. 3 and 4, the current catalyst compounds improvethe removal rate of a 30 wt % MEA acid gas scrubbing solvent.

Catalyst Testing in Concentrated Primary Amines: WWC Method

The wetted wall column (WWC) is used to determine mass transfer of CO₂into a process absorption solvent. The WWC apparatus is illustrated inFIG. 5. The improved overall mass transfer resulting from the use of twocatalysts is illustrated in FIG. 6.

In each test, solvent is loaded to a molCO₂/molN level of approximately0.1 with CO₂ by sparging the solution reservoir with a concentratedCO₂/N₂ mixture. The initially loaded solution is then circulatingthrough the wetted wall column and a pre-heater which heats the solutionto the desired temperature. Once the solution is thermally stable, asimulated flue gas stream (CO₂ balanced with N₂) saturated with waterflows into the wetted wall column. In the wetted wall column, liquidflows downwards on the outside surface on an annular tube while CO₂ gasstream flows upwards around the annular tube. CO₂ absorption from thegas phase into the liquid takes place along the tube's wall. Gaseffluent from the WWC is dried and analyzed by an infrared CO₂ analyzerfor CO₂ concentration determination. CO₂ inlet concentration is analyzedby directing the gas stream to bypass the WWC. A liquid sampledownstream of the WWC is collected at each solution carbon loading andtested for total liquid CO₂ loading, viscosity, density, and pHmeasurements. Liquid film thickness is calculated by Eq. 1. The bulksolution is then loaded with more CO₂ and the data collection cycle isrepeated

$\begin{matrix}{\delta = \sqrt[3]{\frac{3\mu\; Q_{sol}}{\rho\;{gW}}}} & {{Eq}.\mspace{11mu} 1}\end{matrix}$in which μ is the viscosity, Q_(sol) is the liquid flow rate, ρ is thedensity of liquid, and W is the circumference of the column.

The overall mass transfer coefficient at the operating condition can becalculated from Eq. 2.

$\begin{matrix}{K_{G} = \frac{N_{{CO}_{2}}}{\Delta\; P_{{CO}_{2}}}} & {{Eq}.\mspace{11mu} 2}\end{matrix}$in which N_(CO2) is the flux of CO₂, K_(G) is the overall mass transfercoefficient, ΔP_(CO2) is the log mean of driving force which is definedby

$\begin{matrix}{{\Delta\; P_{{CO}_{2}}} = \frac{P_{{CO}_{2}}^{in} - P_{{CO}_{2}}^{out}}{\ln\left( \frac{P_{{CO}_{2}}^{in} - P_{{CO}_{2}}^{*}}{P_{{CO}_{2}}^{out} - P_{{CO}_{2}}^{*}} \right)}} & {{Eq}.\mspace{11mu} 3}\end{matrix}$in which P_(CO2) ^(in) and P_(CO2) ^(cut) represent the CO₂ partialpressure at the inlet and outlet of the wetted wall column, and P*_(CO2)is the equilibrium partial pressure of CO₂. The P*_(CO2) is obtained bymaking the flux N_(CO2) to be zero at zero driving force and solving the2 equations simultaneously using a trial-and-error routine in MATLAB®.

The foregoing has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theembodiments to the precise form disclosed. Obvious modifications andvariations are possible in light of the above teachings. All suchmodifications and variations are within the scope of the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

What is claimed:
 1. A method of increasing overall mass transfer rate of acid gas scrubbing solvents, comprising: adding a catalyst compound to a fluid stream including an acid gas and an acid gas scrubbing solvent, said catalyst compound having a chemical formula:

where: (a) M is any group VII B through XII B element; (b) E is a combination of N with O and/or S having a net 2⁻ charge per individual ligand with N positioned as set forth in (i); (c) R_(1, 2, 4)=—H, —COOH, —[OCH₂CH₂]_((n1))OR₉, amine, amide, phosphate, —OH, —R₅OH, —[SO₃]⁻; (d) R₃═—H, —COOH, —[OCH₂CH₂]_((n1))OR₉, amine, amide, phosphate, —OH, —R₅OH, —[SO₃]⁻, —[(CH₂)_(n)Q]⁺[A]⁻; (e) R₅═C₁- C₅ alkyl; (f) A =monovalent anion: CI, Br, I, F, PF₆, BF₄, acetate, trifluoroacetate, CIO₄, NO₃; (g) Q=monovalent cation: PX₃ where X=alkyl, cyclic alkyl, aryl, O-alkyl, O-aryl, N(R₆)₃ where R₆=alkyl, cyclic alkyl, N-heterocyclic ring, imidazole; (h) n₁=1 to 10; (i)

where Y═—H; —COOH; —R₇OOH where R₇ is an alkyl ranging from 2-10 carbons; —[OCH₂CH₂]_(n)—OR₉; —OH; —SO₃; —NO₂; amine, amide; or selecting from the group consisting of

where Z₁₋₆═—H; any alkyl; —COOH; —R₈OOH where R₈ is an alkyl ranging from 2-10 carbons; —[OCH₂CH₂]_(n)—OR₉; OH; SO₃; NO₂; amine, amide; (i) R₉═H, or alkyl.
 2. The method of claim 1 wherein said catalyst compound has a chemical formula:

where R =any alkyl M=Co, Zn.
 3. The method of claim 1 wherein said catalyst compound has a chemical formula:

where M =Co, Zn.
 4. The method of claim 1 wherein said catalyst compound has a chemical formula:

where M =Co, Zn R =any alkyl.
 5. The method of claim 1 wherein said catalyst compound has a chemical formula:

where M =Co, Zn.
 6. The method of claim 1 wherein said catalyst compound has a chemical formula:

where M =Co, Zn.
 7. The method of claim 1 wherein said catalyst compound has a chemical formula:

where M =Co, Zn.
 8. The method of claim 1 wherein said catalyst compound has a chemical formula:

where M =Co, Zn.
 9. The method of claim 1 wherein said acid gas scrubbing solvent includes an amine.
 10. The method of claim 1, wherein said acid gas scrubbing solvent includes a mixture of a primary or secondary amine and a tertiary amine.
 11. The method of claim 1, wherein said acid gas scrubbing solvent includes a material selected from a group consisting of monoethanolamine (MEA), 1-amino-2-propanol (1A2P), 3-amino-1-propanol, 2-amino-1-propanol, 2-amino-1-butanol, 1-amino-2-butanol, 3-amino-2-butanol, 2-(alkylamino)ethanonol (MAE), diglycolamine, morpholine, piperazine (PZ), 1-methylpiperazine (NMP), 2-methylpiperazine, hydroxypiperadine, hydroxyalkylpiperazine, 2-piperidineethanol, N-aminoethylpierazine (AEP), aminopropylmorpholine, 4-aminopiperidine, 3-aminopiperidine, 2-amino-piperidine, diethanolamine, 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA), diisopropanolamine (DTPA), glycine, alanine, ß-alannine, sarcosine, isopropanolamine, benzylamine, methyldiethanolamine (MDEA), triethanolamine (TEA), alkali carbonate, N,N,-dialkylethanolamine, N,N,N′,N′-tetraalky-1,8-naphthalenediamine, N,N, -dialkylbenzylamine, 1,4-dialkylpiperazine, N,N,N′,N′-tetraalkyl-1,6-hexanediamine, N,N,N′,N′-tetraalkyl-1,5-pentanediamine, N,N,N′,N′-tetraalkyl-1,4-butanediamine, N,N,N′,N′-tetraalkyl- 1,3-propanediamine, N,N,N′,N′-tetraalkyl-1,2-ethanediamine, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenedia mine, N,N,N′,N′,N″-pentaalkyldiethylenetriamine, N,N,N′,N′,N″-pentaalkyldipropylaminetnamine, N,N,-dialkylcyclohexylamine, N,N,N′,N′-tetraalkylbis(aminoethyl)ether, N,N,-dimethyl-2(2-aminoethoxy)ethanol, where alkyl represents any methyl, ethyl, propyl, butyl isomer, and mixtures thereof.
 12. The method of claim 1, wherein said catalyst compound is provided at a concentration of between about 0.05 mM and about 100 mM. 